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Q&A: Powdery Mildew on Zinnias
National Gardening Association
Question: The leaves of my zinnias have white spots on them, which
seem to gradually enlarge. A few of the plants have died and the
others are struggling. What are these white spots, and did they kill
the plants? What can I do about it?
Answer: It sounds like powdery mildew, which many zinnias are susceptible to. Powdery mildew appears as a whitish/greyish powder on foliage. It overwinters on living plants, and can be difficult to eradicate. If the zinnia plants are declining rapidly, you may want to simply remove them. It's unlikely you'll be able to control the disease in time for these heat-loving plants to recover and put out more flowers before cool weather sets in.
There are some things you can do to minimize its effects next season. The first line of defense is to grow resistant varieties. Also, be sure to space plants properly for good air circulation, and thoroughly clean up plant debris at the end of the season.
Powdery mildew is unique among common plant diseases in that it doesn't require a wet leaf surface to spread. It can thus thrive during hot, dry weather, which is why you see it appearing in August. The general advice to inhibit the spread of fungal diseases is to avoid wetting leaf surfaces. In the case of powdery mildew, you can actually inhibit infection with frequent sprays of water. Also, examine plants frequently, removing any affected foliage immediately.
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Posted Comments:
08-27-2008 09:53
JN KOSS wrote:
POWDERY MILDEW
i'VE BEEN USING A CLOSED END SPRAYER FILLED WITH
BAKING SODA. IT SEEMS TO WORK FOR ME.
JIM
BAKING SODA. IT SEEMS TO WORK FOR ME.
JIM
08-26-2008 17:59
Jackie wrote:
Inhibiting the powdery mildew
What you are saying makes no sense!! First you say that you can inhibit the spread of powdery mildew by avoiding getting the leaves wet! Then you said you can inhibit powdery mildew by spraying the Zinnias with water.Since Powdery mildew is on the plant HOW IN THE WORLD CAN YOU SPRAY THE PLANT WITH WATER WITHOUT GETTING IT WET? You did not mention that there ARE good fungicides out there that will help. Ortho and Scotts both have them.
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